Wireless receiving system



y 2- N. RITTENHOUSE 1,860,592

WIRELESS RECEIVING SYSTEM Filed Sept. 22, 1926 2 Sheets-Sheet 1 May 31, 1932. N. RITTENHOUSE 1,860,692

WIRELESS RECEIVING SYSTEM Filed Sept. 22, 1926 2 Sheets-Sheet 2 g By A tiorneys,

I I INVENTOR Patented May 31, 1932 Application filed September 22, 1926. Serial No. 137,038.

The present invention relates to improvements in the construction, arrangement and connections of electrical apparatus for wireless reception. The ob ect of th1s 1nvent1onis to provide a receiver having at leastone stage of radio frequency amplification ahead" of the detector stage, the stabilization of which radio frequency amplifying-stage is under the control of the operator, is very easily adjusted and provides an extremely stable radio frequency amplifying unit over a Wide band of broadcast frequencies, yet at the same time permitting very high amplification at every-frequency for which the receiver is designed.

The detector may be of any known type and amplification preceding the detector stage may be obtained by audions or vacuum 7 tubes adapted to be operated on'either alternating or direct current employed for the direct electrical heating of the electron-emitter element or for indirectly heating such element. I

An important feature of the invention resides in the provision of anindependent stabilizing circuit which connects the grid and electron-em1tter element of an aud1on which is to be stabilized, this stabilizing circuitbef ing so arranged as to exclude all batteries, or other current supplying means, condensers, coils and other electrical elements through i which the current of other essential circuits; must flow, it being necessary only to qualify this statement to the extent that the stabilizing circuit may be said to makeuse of the simple conductors or leads connected to the audion in commonzwith other circuits. 5 It will be noted, however,that asto such conductors there is no appreciable'impedance or reactance which could cause any undesirable interaction between the stabilizing current and thecurrent flowing in any other circuit;

This isolation of the stabilizing circuit hasbeen found to give greatly improved results as compared with stabilizing systems where-- in the stabilizing or neutralizing circuits have included electrical elements, such as batteries, condensers, etc. which provide a common path for both the stabilizing current and also the plate or grid currents of the audi ons. The stabilizing system according'tothe present invention is not critical in adjustment and permits'a very smooth. and gradual rege ulation of amplification. Furthermore, when adjusted to obtain practically the maximum-v amplification "the circuit is'not' inthe usual criticalcondition, and severe static and other 1 stray disturbances do notjcause theaudion circuits to break into uncontrolled oscillation which ordinarily givesyrise to theTfamiliar squeal or hetrodynenote. In the operation of the receiver it is alsoobserved that practi-;

cally no greater movementofthe stabilizing" control is necessary-to stop uncontrolled os cillation than is required to startit, so that if the critical setting is exceeded the objectionable oscillation is stopped by :a 'very slight reverse movement of the control. Thisv characteristic is'of material advantagein" picking up very weak signals which, in the usual receiver employing regeneration in the radio frequency stage, are only audible at the most critical setting of the regeneration control. For such receivers the'weak signals become inaudible when the control is'turned back a suificient distance to check excessive oscillation once the circuitwhas .spilled' over, whereas in the present apparatus the stant that such oscillation ceases. This unique characteristic may perhaps be best. described as one of flexibility of control, since it renders si'mpleand facile, an adjustment which has hitherto required considerable skill and nicety ofmani'pulation;

The radio frequency" amplifying circuit signal'becomes' audible practically at the inhereinafter tofbe particularlyrdescribed is' applicable, to aiwide variety of wlreless recelving apparatus. The method of stabilizingtheradio frequency amplifying circuit is applicable. to receivers employing a plurality of radio frequency amplifying stages before the detectorv stage. j

The invention further contemplates means for effectively byI-passing radio frequency current around'the'plate current supply of, the radio frequency amplifyingstage,which current supply is com1non,at least inpart, to the filament plate circuits of other audions; in'the receiver, whereby to eliminate as far as possible the presence of radio frequency current in the audio amplifying circuit.

It is well understood that in'radio frequency amplifying circuits employing audions or vacuum tubes, much difiiculty is experienced in preventing uncontrolled oscillation and at the same time maintaining a high amplification. This difficulty is due in part to the capacity effects between the elements of the vacuum tube itself and also to the capacity and magnetic coupling between the various coils and leads which necessarily constitute a part ofthe receiving circuit. Because of the impossibility of effectively isolating various elements of the receiving circuit, energy is transferred from one part of the circuit to another in a manner which in an efficient receiver almost inevitably results in a condition of instability, the circuit hav ing a pronounced tendency to break into selfsustainedoscillation. This tendency must, be counteracted'in order to permit of the reception of broadcasting.

A numberof systems have already been devised for the purpose of stabilizing the radio frequency amplifying stages. One method is .tocontrol the grid potential by means of a potentiometer, another to-control the brilliancy of the filament in the vacuum tube. According to another system a tickler.

coil inserted in series with the filament plate circuit is inductively related to the input circuit in such manner that a negative feedback takes place, this feedback being controlled by varying the coupling between the two circuits to effectively suppress local oscillations in the radio frequency amplifying tube; Still another method contemplates the suppression of local oscillation in the radio frequency stages by tapping the secondary winding of the interstage transformer coupling'any two successive stages, such as the first and second radio frequency amplifying stages orthe second amplifying stage and the detector, and leading a portion of the energy developed in the secondary winding of such transformer back through a small condenser to the grid of the tube which feeds the transformer. This latter method of stabilization characterizes the neutrodyne circuit in which or inductively coupling to such circuits various energy-absorbing means, but such methods are not efficient and generally result in losses which render the radio frequency i amplification stage of relativelysmall value. 7 In practice it has been found, generally speaking, that stability and ease of control of the radio frequency amplifiershave been obtained at the expense of amplification and sharpness of tuning.

The present invention provides a receiving apparatus having one or more stages 'of radio frequency amplification in which effective stability is obtained with relatively lowlosses in the amplification, the receiver at the same time having unusually high selec-' tivity. While more than one radio frequency amplifying stage may be employed, this is not necessary because with an 'efiicient' antenna the amplification obtainable in a single stage,

according to the present invention, is as high as the static level will permit. That s to say, a single stage of radio frequency amplification will satisfactorily amplify a signal so weak, thatit is almost useless-because of the relative intensity of static disturbances and other .strays which are present under the most favorablereceivingconditions. It will therefore be understood that the efiiciency of the present system is exceedingly high since the great majority of modern receivers require at least two radio frequency stages, and in many instances more than two stages to. obtain this result. Thecircuit, furthermore, possesses the highest selectivity theoretically obtainable because it is possible to so sharply tune the receiver that portions of is combined witha detector circuit having the usual hard vacuum tube as a detector and a three-stage resistance coupled audio ampli- Further obj ectsof the invention wii hereinafter be pointed out in connection with the. detailed description of theinvention, refer; ence'beinghad to the accompanying drawings, in which, Figure l'is a circuit diagram of a radio receiver employing one stage of'radio fre-, quency amplification, a detector stage and three resistance coupled audio amplifying stages. r i Fig. 2 is a perspective view of the special threev winding transformer and stabilizer which couples the radio frequency stage to the detector and serves as a source ofstabiliztions, the radio frequencyamplifying circuit ing energy'for the radio frequency amplifying circuit. I

Fig.8 is a'circuit diagram ofareceiver-employing two stages of tuned radio frequency and a'detector, noaudio frequency amplificm tion being shown. v

In the embodiment illustrated in Figure "1 a radio broadcast receiver accordingto the present invention comprises a radio fro-Q quency amplifying stage generally desig: n'ated'by R. F, a detector circuit 'D and three stages ofresistance co'upled audio ampliiication designated respectively-as A. F

A. F and A. F9. An inductance L, shunted by a variable condenser G constitutes the tunedcircuit of the radio frequency aniplie fyiiig stage. The'inductance coil L is preferably tapped at three points towardsits lower end, as illustrated atl, 2 and 3, to provide for a direct'connection of the antenna at on of the three points. This pro-.

vides what may be termed a semi-tuned antenna circuit, the incoming energy fromthe antenna a passing through more or less of the tapped inductance L and thence directly to the ground g. The antenna connection with inductance L at various points may be effected by any suitable switching device such as a three point switch S, the contacts of which are connected to the three taps re ferred to. The elements which distinguish the present radio frequency amplifying circuit from other known devices are incorporated in what may be termed a combination radio frequency transformer and stabilizing unit diagrammatically indicated in Figure 1' which is successively woundtl e three windings S, P and S respectively. The primary and stabilizing windings are preferably placed near the filament or low potential end of the secondary winding. The windings are preferably wound in the same direction and connected to the various leads, as indicated in the diagram. It will be understood thatthe description of this transformer and stabilizing unit is in certain respects merely illustrati ve and that other arrangementswhereby' three: windings may be inductively related and employed for the purposes herein specified, falls Wlllllll'ltllG scope of my invention.

For example, it has been found thatsatis-l factory resultsmay be obtained by winding the stabilizing winding directly on the secdistance therefrom. i ever, that the primary and secondary w ndings be closely coupled, and forthis reason.

perspective, is shownin ondary, and windingthe primary ontop of.

the said'stabilizingwinding. Except for the niechanicaldifiiculties of fabricating the unity,

the stabilizing winding and primary may be disposedwithin thesecondary. Further more, it is not essential that the primary and stabilizing windings be placed close to the filament or lowpoten'tial end of thesec ondary winding, but maybe locatedsome It is important, .how

they are wound in such manner as to be rad ally overlapping and are not separated by a large a r gap as is customary in the majority of commercial receivers. To obtain maximunrcoupling'it is importantthat the high potential terminals of the primary and secondary windingsbe of the same polarity,

as will hereinafter more fullyappear] In? thejpastit has been customary to arrange the transformer 'windings'so that the high-po-i tential terminals are of opposite polarity, with the particular object of reducing the coupling so as toachieve a condition of,a'uto.-x riatic stability over a predeterminedrange of-operating frequencies but at the sacrifice" 'of efficient amplification. The windings 'P and S, considered alone, constitutethe radio frequency transformer whereby the output ofithe radio frequency tube r is delivered to the detector cl. In addition to this usual transformer arrangement, howeverya thirci winding, which I have designated a stabiliz ing winding S, is closely coupled to the two quencytransformer. There is induced in this winding a fluctuating potential which is de pendent upon the combined magnetic flux ofthe two coils P and S; p

The upper end of the stabilizing coil S is connected to the filament lead of the radio frequency tube r, as shown in Figure 1. The lower end of the stabilizing coil is connected through a small variable condenser C 'with' the grid lead of this tube. 'The upper) or winding P and secoiidary'winding con nectedrespectively to the plate and grid leads thigh potential terminals of the primary of the vacuum tubes 1 and (Z, while thelowpotential terminals of'said windings are connected to the filament systems ofisaid tubes.

The lower terminal of the secondary windings connects directly with the filament sys-.

tem while the lowerf'end of the primary P is connected therewith through the plate cur-v izu rent supply,jthe terminals employed for this i connection being marked respectively B.

and'AB in Fig. 1. 'It'will thus be seen that the plate terminal of the primary 7 winding P and the grid: terminal of thesecondary winding S are disposed relatively to ward the same end of the windings, i. e., to l; ward-the high-potential ends, and said termina'ls are- 0f the same-polarity: Thisre=a 100 windings Band S constituting'the radio fre sults in obtaining a much closer coupling between the primary and secondary windings than if their high-potential ends were of opposite polarity. This very close coupling permits of the maximum transfer of energy from primary to secondary windings and accounts in considerable measure for the remarkably .high efliciency of the receiver according to uum tubes employed. The large number of tubes in modern receivers is to a considerable extent necessitated by the ineliiclency of the circuits, efliciency having been sacrificed to obtain stable operating characteristics.

In the circuit according to the present invention high efiiciency is achieved, and controllable stabilizing means are provided which permit the utilization of such efficiency" to the fullest extent over the entire range of broadcast frequencies whenever weak sig nals are to be picked up. In other words, instead of providing a receiver that wastes a sufficient amount of energy to render the circuit automatically stable at all frequencies in'thebroadcast band, I utilize a circuit in which the efliciency is preferably such that automatic stabilization can not be achieved at all broadcast frequencies and provide means for adjusting the stabilization in accordance with the frequency which is being received. This adjustment is unnecessary when receiving strong local signals because the tubes are then only required to operate at low efficiency and the tendency toward self sustained oscillation can be effectively suppressed by reducing. the filament voltage in the detector and radio frequency stages. The proper value for the windings P, S and S once having been determined, the combi nation transformer andstabilizing unitgenerally designated by A, is preferably assembled as a fixed part of the apparatus, no

adjustment being thereafter required in the inductance or coupling of the three elements thereof. the term filament is employed herein the word is used generically to indicate the elec tron emitter element which cooperates with the plate of the vacuum tube to provide a path for the plate current, the flow of which is regulated by the grid potential in a wellknown manner. The filament need not be in the form of a wire nor need it be heated would It will be understood that wherever by current which passes directly there-. through.

The stabilizing winding S is so related to the transformer windings P, S-that there will be induced in the former a fluctuating current, which, if properly controlled by the variable capacity C will efiectively oppose the action of electrostatic coupling between the elements of the vacuum tube and stray coupling between other portions of the receiving circuit, whereby the capacity for, self-. sustained oscillation within the circuitmay be entirely eliminated.

In properly designed apparatus according to the present invention, the control of amplification throughthe adjustment of the stabilizing condenser 0 while not critical, is extraordinarily eifectlve. It 18 possible for one who 18 not skilled 1n the handling of recelvlng apparatus to obta n practically the maximum possible amplification, taklng full advantage of the inherent amplifying power of theradio frequency stage. 'As is well understood in' most radio receiving apparatus, the adjust ment of the control which suppresses self sustained oscillations is very critical. To obtain anything like efficient results the control must be adjusted to a point very close to the point of oseillationand yet must not reach this point, or the signal which is desired will be obliterated. By virtue of the novel design and relationship of the various elements in the present receiving apparatus, an unusually highdegree of inherent stability of the radio frequency circuit is obtained without recourse to wasteful energy-absorbing means. At the same time the circuit can berbrou'ght practically to the peak of possible amplification and will remain in continuous operation very close to this peak regardless of disturbances such as heavy strays or wide fluctuations in signal intensity without danger of spilling over or breaking into self-sustained oscillation. Such oscillation practically destroys thebroadcasting whichit is desired to receive, and not only gives rise to objectionable squeals and howls at the receiver, but in most instances, re-radiates oscillating energy from the antenna, which is highly dis- *turbing to neighboring receivers.

The explanation which at this time seems best toaccount for the unusual operating characteristlcs of this receiver is the fact that the stabilizing coil S is conductively independent of either the filament-plate circuit of the radio frequency tube or the grid circuit or connections therewith in the detector stage. In the well knownneutrodyne circuit the stabilizingenergy whichis fed back to the grid of the radio frequency tube is tapped off from a point between the ends of the secondary winding of the radio frequency transformer. As ,a consequence of this, whatever current changes occur in the secondaryv of the transformer which feeds the nseogcoa detector are conductively carried to the lieu tralizing condenser and thence tothe grid of the radio frequency tube.

' In another well known system hereinbefore mentioned, energy is fed back to the grid of a radio frequency tube inductively through a tickler coil which is directly andconductively included in the filament plate circuit ofthe radio frequency tube:

I am. not aware of any systemin which a conductively independent stabilizing winding is inductivelycoupled to the primaryand secondary of a radio frequency transformer and is utilized as a source of energy supplied to the grid or other related parts of the radio frequency circuit whereby to counteract the inherent tendency of a tuned vacuum tube circuit to generate self-sustained oscillations.

Because of the effectiveness of the stabilizing'control it has not been found necessary to reduce'the number of turns on the primary winding P whereby to reduce the tendency toward oscillation, with a consequentloss' of efiiciencyin the transfer of energy between the primary and secondary-windings of the transformer. This is'a wellknown method of obtaining stability in the radio frequency amplifier but results in low eflicienoy. I

The detector stage of the receiver illus trated in Figure 1 difiersf from usual practice in certain respects; The fixed capacity C is shunted across the B battery-supply to theplate circuit and alsothe resistance element or resistorR of the audioamplifying circuit. The transformer secondary-S- which feeds the detector .grid forms an integral part of the combined transformer, and sta bilizing unit A, as has hereinbeforerbeen pointed out. The secondary'winding "S-is tuned in the usual manner byavariable condenser C Detection is accomplished preferably by the usual hard vacuum tube, in the grid lead ofwhich is placed agrid. condenser C4; around which is shunted a high-resistance grid-leak The detector stage in the preferred embodiment of my inventionisnonregenerative and is so designed that self-sustained oscillationscan not be set up therein.

Itnhas been found difficult to eliminate distortionwhere any high degree of regeneration is employed in v the detector circuit, and the present. radio frequency amplifying circuit is so efiicient thatfurther amplification in the detector is not necessary.

To'eliminate, as far as possible, distortion of any kind, and at the same time secure ample volume for ordinary loud speaker opera tion, three stages of resistance coupled audio amplification are preferably used. The first two audio frequency amplifying tubes a jand a may be of the usual 201 A or 301A type.

The third audio amplifying tube a is preferably a tube of higher capacityor what isnow termed a pow-er tube,vwhich is capablezof handling relatively large energy for effective loudspeaker operation withoutndanger of overloadingandconsequent distortion of the broadcast reception. r'lhe design: of theresi'stance coupled audio amplifier, generally speaking,fzcorresponds with usual F practice. There are two features which depart from known methods, howeven: One of these is theconnecting. together the filament controls of p the detector and audio frequency amplifying tubes. This has not,:.tomywknowledgeybeen possible heretofore. Because of-the unusual stabilityiofthe' presentzreceiver it is feasible toxconnect the filaments-of any orzall ofathe vacuum tubes in the system; together and con: trol the current flowing; through such tubes. by acurrent limiting device common to all,=no individual 1 filament; control J being j required whereby:toiindependentlyvary the filament brilliancy-of the-detector tube. with respect to" the audio frequency tubes. In the construet onv illustrated in Figure 1 a single automatic ballastz nesistance iR is-zemployed-g to control the'filaments of thedet'ectorand the first "and second audio: frequency amplifying tubes. A. second: ballast; resistance 1R is employed to control the. filament" of the power tube in the third'waudio frequency stage becauseof'the fact thatgitis-often desirable, when great volllme 1s 'not requiredg'to cut out'theipower tube andoperate only. on two stages of resistance coupled,audioamplification. The radio frequencytubamayfbe{controlled by. a. single. resistance such-as R inycommon'lwith the de-.

tectorandaudio frequency amplifying tubes However, an independentvariable resistance siis preferably employed. J

.Noindependent. switches arerprovided for;

the"varioustubes,all of the tubes being {under the control of-thetwo automaticcircuitjacks J and 'J -respectively which are-connected" as-indicated in: theediagram Fig.1. By. thisv arrangement :the'receiver maybe operated with or without the last stage of audio fre-f quenc-yamplification in which the power tube a and fourtube or fivetube operation'isobtainedsimply'by inserting the phone plug in the desired jack. If thereproducer is not plugged into either jack-none of the tube fila- V mentsis lighted. JIf-the. plug is inserted in the first jack J the first; four tubesr, 03,0

andsa are lighted," the power tubes a? receiving no A battery current. 1, If the plug is inserted in thexsecondujack J the filaments of'all five tubes are lighted and-the circuits connectedffor five tubev operation. This arrangement has the advantage of. eliminating L i the telephone or-loud speaker jacks. :By this arrangement the operator knows at a glance whether any of thetubes are lighted or not;

by simply observing whether the plugis in.-

serted ineither ofthe jacks. 'Oneaneed not the filament controlling switch or switches Y which ordinarily .ope'rate'iindependentlyof to the receiver, the receiver is in operation, and when the loud speaker plugis w thdrawn, the set is out of operation and drawing no current from the batteries. This greatly reduces the possibility of inadvertently leaving a filament control switchclosed, with consequent waste of both A and B battery current when the receiver is not in use;

"across the entire block of B batteries feed ing the plate circuit of the power tube a and also the jack J 2 feedingthe reproducer'. That is to say, the condenser serves as a by-passaround both the loud speaker and fB bat tery. 1 The position of capacity G in the circuitis a' departure from usual practice.

In constructing a receiver according to the present invention'the coil L is disposed with respect to the combination transformer and stabilizing unit A in such manner as to reduce as far as possible stray coupling,

either electromagnetic or electrostatic, be

tween the'two. This is accomplished by placing the two elements some distanceapart,

and with their magnetic axes at-right angles to eachother. Stray coupling may, of course,

be further reduced by shielding the elements in individual metallic cages, which are pref erably grounded, but the circuit does not re quire such shielding in order to obtain stability.

The stabilizing method hereinbefore. described is, as has already been pointed out, applicable to multistage radio frequency amplification, a modified circuit incorporating two stages of tuned'radio frequency ampli fication being diagrammatically illustrated inFig. 3. It willbe observed that the additional stage of radio frequency amplification follows usual practice except that a second combination radlo frequency transformer and stabilizer unit'A is interposed between the two stages of amplification. The other 7 details of the circuit need not bedescribed as 7 they follow practice which is entirely familiar to thoseskilled in the art. 7

To render the disclosure of my invention more complete and to facilitate its practical application by those skilled in the art, I will give the characteristics of the various elements which I'h'ave found to give the best results for wave lengths between 250 and 500 meters, The tuning coil L and the combined transformer and stabilizing coil A in the embodiment shown in Fig. 1 are both wound on cylindrical forms approximately three inches in diameter. -The tuning coil L is made up of 57 turns, the coilbeing tapped at the third, seventh and eleventh turn respectively, for rough antenna tuning; The combination transformer and stabilizing [unit shown in perspective in Fig. 2 comprises a primary winding Pof ten turns, a secondary winding of '59 turns and a stabilizing winding of 9 turns. The values for the other elements in the circuit, are as follows:

0 .00035 microfarad l about 15 micromicrofarads (commercially known as a midget condenser) C, .00035 microfarad C .00025 microfarad C .002 microfarad C 1 inicrofarad R 2-.5 megohms The values of the resistances in'the audio frequency amplifying ircuit will, of course,

vary with the'type of tube used, as well as the filament control resistances,which may be of the manually 'variabletype or the automatic ballast resistance. If a power amplifying tube is employed in the last audio frequency stage, a C battery X should be employed in accordance with of the tube used. 1 a

The operation of .the five tube receiver shown in Figure 1 is very simple, only two of the variable controls requiring adjustment 7 for local reception. If extremely weak signals are to be received, adjustment of the stabilizing control is requiredand also approximate tuning of the aerial circuit by the selecthe characteristics tion of the tap on the inductance L best z suited to the desired'wave length. To place the set in operation it is only necessary, as before described, to insert theloud speaker plug or phone plug, as the case may be, in

either jack J or J depending upon whether four tube orfive tube operation is desired.

If local stations only are to be received,thc

stabilizing condenser C is set in a position to insure freedom from local self-sustained oscillation in the radio frequency stage and the various stations may be tuned in by simply adjusting the two variable condensers C and frequency will be substantially the same. 7 The dials of these condensers maybe frictionally coupledtogether in accordancewith known practice whereby the two condensers will be adjustedin unison. No attentionneed be paid to the filaments of the detector and audio frequency amplifying tubes, as in the present receiver. These tubes are controlled by automatic filament ballast resistances R and R The rheostat R controlling the fila- 1', once adjusted to give the best results, need .0 the dial settings of which for any given ment of the radio frequency tube or audion not be again altered so long as the filamentvoltage supply remains substantially the same. 1

To pick up very weak'signals the proper tap on inductance L isselected for the desired frequency and the condenser .C -is adjusted to a position in which a beat note is heard, when the condensers G and (lg-are set for the desired frequency; This beat note is 7 due to theself-sustained oscillation within the radio frequency stage in combination with the carrier wave which is being received. W' hen the tuning condensers C and C are adjusted to a position which gives the lowest frequency beat note, the .stabilizing capacity control is moved back to a position where the beat note disappears, indicating' thatself-sustained oscillation within the receiver has been suppressed. Once these various adjustments for a givenstation have been determined, the station canalways be again picked up on its characteristic frequency by setting the various controls in the determined positions. i That is tosay, each of the controls can be logged for any given frequency, and by placing the controls in the i logged positions the receiver willbe accurately tuned for this frequency. This statement transformer comprising primary and secholds true for the stabilizing control efiected through the. adjustment of condenser G which is provided preferably witha graduated dial as are the ordinary tuning condensers. ,7 I r In the appended claims the term audion is employed to designate any'form of thermionic valve in which is included an electron emitting element, a positively charged plate or collector for the electrons, and a grid controlling the flow of electrons from said element to said plate; and the term filament is employed in the generic sense to indicate any heated electron emitting element whether it be heated directly by the action of an electric currentor otherwise.

While the invention in its preferred em bodiment has been described and illustrated, it is to be understood that the invention may be modified and otherwise embodied without departing from the spirit of the inven- :tion, as set forth in'the'following claims.

What I claim is: r e

1. In awireless receiving apparatus employing audions, a stage of tuned radio fre- V quency amplification, a detector stage, a

ondary windings inductively coupling said stages together, the said primary and secondary windings being so arranged that the high-potential terminal of the primary winding is of the same polarity as the highv potential terminal of the secondary winding, and an independent stabilizing winding in the magnetic field of said transformer, one end of said winding being connected directly to a filament lead of the radio frequency a'udion 'and the' other end of said winding being connected through a variable condenser tothe'grid ofsaid audion. 1 2. In a wireless receiving apparatus employing audions, a plurality of tunedstages of radio frequency amplification, aftransondary windings beingso arranged thatthe V high-potential terminal of the primary Winding is of the same polarity as the high-poten-' 1 v tial terminal of the secondary winding, and an independent stabilizing winding and circuit therefor which does not include any winding or condenser constituting a part of 7 the tuned inputcirc-uit of any of said stages, sa1d wlnding being lnductlvely coupled to the windings of saidtransformer, and. adapted to feed back energy directly to the grid of the audion ofthe first ofany two succes sive stages of amplificatlon and 1n a d1rec-' tion to suppress self-sustained oscillations in such stage, the connections being such that the resistance and stray field pick-up of the filament plate current supply means isex cluded from the sa1d circult of the stablli'zlng wlndlng. r r

3. In a wireless receiving apparatus em ploying, audions, a plurality of stages of radio frequency amplificat on, a transformer, comprising primary and secondary wlndlngs inductively icoupllng successive stages'together, the said primary and secondary windings being so arranged that the high-' potential terminal ofthe primary winding is ofthe same polarity as the high-potential terminal of the secondary winding, andan independent stabilizing winding inductively coupled to the windings of said transformer,

a condenser in series'with said stabilizing winding, the said stabilizingwindi'ng and condenser being connected between the grid of the audion of the said first stage ofamplification and a filament lead of such by simple-metallic conductors,

4., In a wi'reless receiving apparatus, a stage of radio frequency audion amplification including the primary winding of aradio audion frequency, transformen. said winding com- 1 prisinga part of the filament-plate circuit" of said stage, the secondary winding of said transformer formingapart 'ofthe tuned grid circuit of the neat succeedingaud'ion, the sa1d primary and secondary windings being so arranged ,that the high potential terminal of the primary winding is of the same polarity as the high potentialterminal of the V secondary windingyand an independent stabilizing winding external to either of the said circuits but inductively coupledto at east one of sai'detransforiner'win'dings and adapted to feedback stabihzing energy di rectly to the grid of said radio frequency audion through an independent circuit which includes a variable condenser, and in each circuit there is no winding or condenser whlch would constitute a part of a tuned input .of the said first mentioned audion .stage' whereby to suppress self-sustained oscillations in said stage.

'ings.

5. In a wireless receiving apparatus employingan audion inthe radio frequency amplifying stage, a transformer comprising vprimary and secondary windings conduced directly between the "rid of the audion of the said radio frequency amplifying stage and the posltlve filament lead of such audlon. 6. in a wireless receiving apparatus employing audions, twotransformer connected audionstages, the transformer having its primary winding in the plate circuit of the first audion and its secondary windingin the grid circuit of the second audion, the said primary and secondary windings being so arranged that the high-potential terminal of the primary winding is of the same polarity as the high-potential terminal of the sec ondary winding, and an independent stabilizing windinginductively related to said transformer windings, a variable condenser connected in series with said stabilizing winding, the last mentioned winding and condenser in series therewith providing a bridge circuit between the gridand electron emitter element of the first audion, and this bridge circuit being disposed so as not to include the plate current-supply means, or

any winding or condenser through which the plate current is directly applied.

7. An electric circuit arrangement for stabilizing transformer coupled audions, comprising a primary winding connected between the pla e andelectronemitter of one audion, a secondary winding connectedbetween the grid and filament of'a second audion, and an independent stabilizing winding and condenser connected in series between the grid and electron emitter of said first-mentioned audion, the said. primary and secondary transformer windings being wound in the same direction and radially overlapping, theplate terminal of the primary winding and the grid terminal of the secondary winding being disposed relatively toward the same end of said 8. In a wireless respective windreceiving apparatus employing audions, a stage of tuned radio frequency amplification, a detector stage, primary and secondary windings inductively coupling said stages together, said primary and secondary windings being so arranged that the high-potential terminal of the primary winding is of the same-polarityas the high-potential terminal of the secondary winding, and a stabilizing winding andvariable condenser connected in series between the grid and electron emitter of the audion in the said radio frequency stage, said variable condenser being provided with a man'- ual control adapted to be readily adjusted in the manner of a tuning control according to the frequency of the impress-ed oscillating current whereby to obtain the requisite de-i gree of stabilization at various frequencies -9. An electric circuit arrangement for stabilizing transformer coupled audions, comprising a primarywinding connected between the plate and electron emittersof one audion,a secondary winding connected be tween the grid and electron emitter ofa second audion, the said primary and secondary transformer windings'being so related that the high-potential terminal of the primary winding is of the .same'polarity as the highpotential terminal of the secondary winding, 7 j

an independent stabilizing winding and variable condenser connected in series between V the grid and electron emitter of "said-first mentioned audion, and a manual control for said variable condenser adapted to bereadily adjusted in accordance with the frequency of the impressed oscillatingcurrent whereby to obtain the requisite degree-of stabilization at various frequencies, such adjustment con-- stituting one of the controls whereby the entire circuit arrangement may be readily advarious frequencies.

In witness whereof I have hereunto signed justed to obtain maximum amplification at '1 

